1. Field of the Invention
The present invention relates to a white balance adjusting device of a video camera. More particularly, the present invention relates to a white balance adjusting device of a color video camera, in which an image output is electrically or optically corrected based on measured color information dependent on a color temperature of external light.
2. Description of Related Art
Japanese Patent Laying-Open Gazette (Kokai) No. 59-144292 or Japanese Utility Model Laying-Open Gazette (Kokai) No. 61-7178 for example proposes a white balance adjusting device of a video camera, in which an image output is electrically corrected based on information of color temperature and a color temperature conversion filter is automatically interposed in an optical path for image pickup when the color temperature exceeds a prescribed value. Such a device has an advantage that color temperature determining operation and filter moving operation, which were conventionally attained by manual handling of a photographer, can be automatically performed.
On the other hand, recently, the minimum intensity of illuminance permitting image pickup means of a video camera to pick up an image is lowered to such a degree as to obtain a sufficient image output even by the light of a fluorescent lamp generally used in homes. A fluorescent lamp as a non-blackbody radiation source has generally a characteristic showing a large proportion of a green color component compared with a blue component and a red component in the emitted light and an image output under the illumination of a fluorescent lamp has a greenish color. Under the circumstances, there is available a non-blackbody radiation correction filter specially used for fluorescent lamp, namely, a fluorescent light correction filter for correcting such greenish output. However, use of such a correction filter in a conventional device is inconvenient since manual operation by a photographer is required to move into or from an optical path of image pickup means based on determination by the photographer as to whether an object is irradiated by a fluorescent lamp or not. Generally, fluorescent lamps of three types having different spectral energy distribution characteristics (namely, a white light type, a daylight type and a three-wavelength type) are used arbitrarily in homes and ratios of the red, green and blue color components in the respective types are different. Consequently, precise white balance adjustment cannot be made only by interposing a fluorescent light correction filter in an optical path.